1. Field of the Invention
The present invention relates to an annular cutter connecting apparatus for connecting an annular cutter to a drilling machine used for drilling relatively deep holes in a workpiece made of a hard material, and an annular cutter connected by such a connecting apparatus to the drilling machine, and more particularly to an annular cutter connecting apparatus for connecting an annular cutter to a drilling machine with ease, receiving only an annular cutter suited for the drilling machine and preventing any annular cutter not suited therefor from being connected to the drilling machine, and such an annular cutter.
2. Description of the Related Art
The conventional drilling machine for drilling a workpiece made of a hard material generally forms holes by driving an annular cutter having downward directed blade edges at a constant rotational speed and feed. Upon drilling a workpiece made of a hard material on this drilling machine, it is necessary to change the annular cutter which is now used when it is not suited for the workpiece to be drilled.
There have been developed various annular cutter connecting apparatuses which facilitate replacement of annular cutters, and annular cutters which can be replaced easily. There are variety of annular cutter connecting apparatuses, the simplest type of which connects an annular cutter to an arbor by means of a blot, and a relative complicated type of which uses locking members such as balls for holding the arbor.
An annular cutter connecting apparatus which has a relative complicated structure as disclosed in Japanese Laid-open Patent Application 62-74515 will be described with reference to FIGS. 1 and 2.
A conventional annular cutter 1 connected to an arbor 2 of a drilling machine (not shown) and transmits the rotation and the feed required for drilling operation from the drilling machine to an annular cutter 8. A cylindrical rotation transmitting member 3 is irrotationally connected to the arbor 2 by means of a key 4. A plurality of holding holes 6 for holding fixing balls 5 are formed in the lateral wall of the lower portion of the rotation transmitting member 3 so as to be directed toward the axis of the rotation transmitting member 3.
On an intermediate portion of the inner peripheral surface of the rotation transmitting member 3 are formed a plurality of engaging portions 7 (FIG. 2) which extend toward the central axis of the member 3 and transmit rotation from the rotation transmitting member 3 to the annular cutter 8. A pushing sleeve 9 for pushing the fixing balls 5 toward the central axis of the rotation transmitting member 3 surrounds the rotation transmitting member 3 so as to be slidable axially thereof. Between the pushing sleeve 9 and the rotation transmitting member 3 is provided a compression coil spring 10 for urging the pushing sleeve 9 downward. The pushing sleeve 9 is held by a holding ring 11 fixed to the outer peripheral surface of the rotation transmitting member 3 so that the-pushing sleeve 9 is prevented from slipping off the rotation transmitting member 3.
The annular cutter 8 has a downwardly open cylindrical body having a plurality of blades (not shown) formed on the lower end thereof. On the upper end of the cylindrical body is formed a cylindrical shank portion 12 inserted in the lower portion of a cylindrical central hole (hereinafter referred to as the "fixing hole") formed by the inner peripheral surface of the rotation transmitting member 3. Axially projecting portions 13 engageable with the engaging portions 7 are formed on the upper end of the shank portion 12. An annular groove 14 for receiving the fixing balls 5 is formed in an intermediate portion of the outer peripheral wall of the shank portion 12.
A center pin 15 for determining the drilled position axially slidably passes through the central hole of the annular cutter 8. An annular engaging groove 16 for receiving engaging balls 17 is formed in the upper end portion of the center pin 15. The annular cutter 8 is connected to the arbor 2 in the fixing hole by pushing the engaging balls 17 into the engaging groove 16. The center pin 15 is urged downward by a compression coil spring 18 through the balls 17, and a sealing member 19 is abutted against the upper shoulder of another annular groove 20 so as to prevent cutting oil from flowing downward from the cylindrical central hole in the arbor 2, when the center pin 15 is not in use. During the drilling operation, however, the lower end tip of the center pin 15 is pressed against a to-be-drilled workpiece (not shown) made of a hard material, and the center pin 15 is pushed in the fixing in the rotation transmitting member 3 against the urging force of the compression coil spring 18. Accordingly, the sealing member 19 is released from the shoulder of the annular groove 20 of the annular cutter 8, and the cutting oil is supplied from the cylindrical hole of the arbor 2 to the blade edges of the annular cutter 8, whereby the drilling operation is performed smoothly.
The annular cutter 8 is fixed to the rotation transmitting member 3 in the following way. First, the pushing sleeve 9 is moved upward against the urging force of the compression coil spring 10. Next, the shank portion 12 of the annular cutter 8 is inserted into the fixing hole of the rotation transmitting member 3 until the projecting portions 13 engage the engaging portions 7. In this state, the pushing portion 21 of the pushing sleeve 9 is displaced from the fixing balls 5, and the fixing balls 5 face the cylindrical ball-escaping hole 22 of the sleeve 9 so that the balls 5 are movable radially outward. Thus, the shank portion 12 of the annular cutter 8 is inserted freely in the cylindrical hole of the rotation transmitting member 3.
When the annular cutter 8 is fully inserted in the rotation transmitting member 3, the pushing sleeve 9 is released. Then, the pushing sleeve 9 is moved downward by the urging force of the compression coil spring 10 and pushes the fixing balls 5 into the annular groove 14 of the shank portion 12. In this way, the annular cutter 8 is fixed to the rotation transmitting member 3.
Upon drilling a workpiece made of a hard material, the annular cutter now on the drilling machine must be replaced by an annular cutter having a diameter suited for holes to be formed, if the annular cutter now on the drilling machine does not have such a suitable diameter.
However, the conventional annular cutter connecting apparatus can connect any annular cutter to the arbor so long as the inner diameter of fixing hole of the rotation transmitting member corresponds to the outer diameter of the shank portion of the annular cutter and the annular groove coincides with fixing balls. Thus, an annular cutter not suited for the driving capability of a drilling machine and for the material of a workpiece is sometimes connected to the arbor 2 mistakenly. If the drilling operation continues without noticing this mistake, unexpected high cutting resistance is produced during the drilling operation. As a result, the driving mechanism of the drilling machine tends to be damaged and/or the blade edges of the annular cutter 8 are apt to be broken.
In case where only blade edges are broken, this problem can be solved by replacing the annular cutter 8 with a suitable one. When, however, the driving mechanism of the drilling machine is broken, the drilling operation must be interrupted for a long time in order to repair the driving mechanism, deranging the production plan. When the annular cutter 8 is not suited for the material of a workpiece, burrs tend to be produced to lower the dimensional accuracy of the formed holes, even if the holes can be formed. As cut chips are wound around the annular cutter 8, the pushing sleeve 9 is sometimes pushed up against the urging force of the compression coil spring 10, and the annular cutter 8 is apt to be adversely loosened or removed from the arbor 2.
When the annular cutter 8 is fixed to the arbor 2 as shown in FIG. 2, the pushing sleeve 9 is lowered so that the annular cutter fixing balls 5 coincide with the escaping hole 22 formed in the lower end portion of the pushing sleeve 9 and are set in a waiting state in the escaping hole 22. In the conventional annular cutter connecting apparatus 1 of a general type, part of each ball 5 projects from the inner peripheral surface of the rotation transmitting member 3 into a central bore defined by the inner peripheral surface of the rotation transmitting member 3 (FIG. 1). Flat faces 23 each having a depth corresponding to the extended amount of each ball 5 into the central bore are formed on the parts of the outer peripheral surface of the shank portion 12 of the annular cutter 8, which parts extend from the annular groove 14 to the upper end of the shank portion 12. When the shank portion 12 is fixed to the arbor 2, the flat faces 23 align with the corresponding balls 5, and then the shank portion is pushed into the central bore.
Any annular cutter can be connected to the arbor 2 so long as the annular cutter is provided with a shank portion 12 having an outer diameter corresponding to the inner diameter of central hole of the arbor 2 and flat faces 23 for receiving the balls 5 extending from the holding holes 6 into the central hole. Thus, the subject matter in that only a suitable annular cutter can be fixed to a specific arbor cannot be achieved by the conventional annular cutter 1.
Japanese Examined Utility Model Application No. 64-3603 discloses one of the conventional annular cutter connecting apparatus which uses a bolt by which an annular cutter is connected to an arbor. This conventional apparatus will be described with reference to FIG. 3. The shank portion 24 of an annular cutter is inserted in the central bore 26 of an arbor 25. Then, a fixing bolt 27 provided in the arbor 25 is turned to engage a flat face 28 formed on the lateral wall of the shank portion 24, and the annular cutter is connected to the arbor 25. The center O.sub.1 of the shank portion 28 should coincide with the center O.sub.2 of the receiving hole 26 of the arbor 25. Actually, however, slight manufacturing errors of the shank portion 24 and the receiving hole 26 and/or fitting tolerances between them produce a center displacement .delta. ranging from 1/100 to 1/50 mm. This displacement provides eccentricity of the annular cutter, giving an adverse effect to the annular cutter.